Problem: If $a + b + 5c = -9$ and $2x + 2y + 8z = 7$, what is $6b + 6a - 18x - 72z + 30c - 18y$ ?
Solution: $= 6a + 6b + 30c - 18x - 18y - 72z$ $= (6) \cdot (a + b + 5c) + (-9) \cdot (2x + 2y + 8z)$ $= (6) \cdot (-9) + (-9) \cdot (7)$ $= -54 - 63$ $= -117$